The present invention relates to a reel position-detecting device for use in a magnetic tape drive unit, and more particularly to a reel position-detecting device for detecting that a tape supply reel has been mistakenly set upside down in a retainer.
Magnetic tape drive units (the recording medium) have been widely used as the external memories of computers. Among these units is a so-called automatic loading magnetic tape unit in which the outer end portion of the magnetic tape wound around a supply reel is guided by high-pressure air to a takeup reel and is automatically wound around the takeup reel. This unit comprises a retainer provided in a tape supply section, and a tape path extending from the retainer to a tape takeup section. When a supply reel is set in the retainer, the retainer rotates in the opposite direction to the tape-supplying direction. Two nozzles are provided, with the retainer interposed between them. These nozzles eject high-pressure air into the tape path. The high-pressure air flow in the tape path draws the outer end portion of the magnetic tape from the supply reel and causes this portion of the tape to extend through the tape path.
A detector means for detecting the outer end of the magnetic tape is provided near the retainer and in the tape path. It can be, for example, a photo-interrupter. When the detector means detects the outer end of the tape, the retainer is rotated in the forward direction, thereby guiding the outer end of the tape into the tape path. Another nozzle is provided within the tape path, for ejecting high-pressure air to the tape takeup section. The air ejected from this nozzle guides the outer end portion of the tape through the tape path to the takeup section.
The tape takeup section has a hub for taking up the magnetic tape. The hub has a slot through which air is sucked into the hub. Hence, when the outer end of the tape reaches the hub, it is sucked into the hub through the slot. While the hub is rotating in this condition, the outer end portion of the tape is wound around the hub. The roll of magnetic tape is thereby automatically loaded in the magnetic tape drive unit.
Since the supply reel has no marks to help a user distinguish one side of the reel from the other, the user often mistakenly sets the supply reel upside down in the retainer. When the supply reel is placed upside down, the outer end portion of the tape extends and bends in the opposite direction, failing to peel off the supply reel, turning many times in one position, or frictionally contacting the inner surface of the tape path and thus being damaged. To make matters worse, the fact that the supply reel has been set upside down is often noticed too late. By then, the tape is usually in a disordered condition when the user becomes aware of his or her error, and it then requires much time and effort to set the supply reel in the correct position.